The present invention relates to the field of radio tuners, and in particular to automatically identifying channels within an AM radio band that include valid audio data.
Conventional AM radio receivers often include the ability to automatically search for radio programs in the AM radio band. The receiver is tuned in discrete steps through the entire AM radio band, and the received field strength at each tunable frequency is determined to provide a measure of the reception quality at that frequency. If the reception quality exceeds a prescribed threshold, the program search is interrupted and the AM radio receiver is set to this radio program.
If the reception quality at the set AM frequency is less than the prescribed threshold, the through-tuning process is continued until either an AM radio program with adequate reception quality is found, or the entire AM radio band has been searched.
A problem with the prior art techniques of finding an AM radio program is that the determination of whether or not a channel includes audio is based solely upon the signal associated with that particular channel. This often leads to erroneously identifying a channel as including valid audio, when in fact the signal on the channel is associated with noise rather than valid audio. Neighboring AM radio channels often spill over to the AM radio channel being investigated, and not only interfere with the signal there but even simulate an AM radio signal with especially high field strength and thus with presumably high reception quality.
Therefore, there is a need for a technique for automatically identifying AM radio band channels that include valid audio.